In a working device for working a work by causing a tool to come into contact with the work, specifically in a grinder for grinding a work by causing a rotating grindstone to come into contact with a rotating work, an AE sensor is used to detect a contact between a tool (grindstone) and a work, detect the completion of dressing of a tool (grindstone) by a dressing tool (dresser), position a tool (grindstone) by detecting that the tool has come into contact with a predetermined reference pin, and detect a collision of a tool (grindstone) with other portions of the working device, etc. AE sensors include various types depending on target frequencies, etc., and an AE sensor used in a working device, such as a grinder, targets an ultrasonic region of tens of kilohertz to hundreds of megahertz and comprises a piezoelectric element, etc.
A case in which a work is ground with a grindstone in a grinder is explained below as an example. However, the present invention is not limited to this, and can be applied to any working device for working a work by causing a tool to come into contact with the work. Further, a case where a contact of a grindstone with a work or dresser is detected is explained as an example. However, the present invention is not limited to this and this invention is also available when working or dressing a work with a grindstone in contact with a dresser.
The AE sensor is widely known as described in NDIS No. 2106-79, 2106-91, etc., and a grinder that uses an AE sensor is also widely known as described in patent document 1 etc., and therefore, a detailed explanation of the AE sensor and grinder is omitted. Only a part that directly relates to the present invention is explained.
Generally, a grinder is arranged in a place where other machines, such as another grinder, are arranged, and the influence of noise from other machines is unavoidable. Further, in a grinder, a work or grindstone is rotating even when the grindstone is not in contact with the work or dresser and an AE sensor detects a signal which has a large intensity even if the grindstone is not in contact with the work or dresser, and therefore, it is necessary to detect a contact between the grindstone and the work or dresser in such circumstances. Therefore, among the outputs of the AE sensor, the components in a frequency range that vary when the grindstone comes into contact with the work or dresser are targeted and the components in other frequency ranges are removed to detect the contact. In a conventional AE wave measurement that utilizes an AE sensor in a grinder, the AE signal is separated from frequency components not targeted using an analog filter. Contact is then detected by determining the power of the AE signal in a range of target frequencies.
Patent document 1: Japanese Unexamined Patent Publication (Kokai) No. H6-114692